Blade coater



J n- 5, 6 c. J. STALMUKE BLADE COATER Filed Feb. 2, 1961 e M w N mm M m m N 0 E T V 6, T N A 2 m .m W G m H m 1 n w Y B m 9 United States Patent O 3,230,928 BLADE COATER Constantine J. Etairnuke, Rurnford, Maine, assignor to Oxford Paper Company, New York, N.Y., a corporation of Maine Filed Feb. 2, 1961, Ser. No. 86,761 12 Claims. (Cl.. 118-413) The present invention relates to blade coaters and is directed particularly to specific improvements in trailing blade coaters.

Oneof the known forms of blade coater, which finds advantageous usein the paper industry, for example, is the so-called' Trist-type coater, in which a chamber cooperates with a backing roll to form a reservoir adapted to hold a supply of coating; material; A paper web is passed around the backing roll, in a manner such that one surface of the paper is in contact with the coating material in. the reservoir. The exit side-of the reservoir is formed in part by a blade which bears against thetravelling paper web and, in effect, meters the coating material onto the web to form a smooth coating layer of desired, uniform thickness.

The conventional Trist-type coater has proven to be arelatively practical and economical. apparatus for coating paper-webs, and has been rather widely adopted by the paper industry for certain types of coating practices. However, one of the very serious limitations of the conventional coater is that it can satisfactorily apply only low coatweights in the range of 3 to 5 pounds per ream,.with. a coat weight of about 7 pounds per ream representing an absolute upper limit for satisfactory operation. The applicationof heavier coat weights, with conventional. apparatus, results in coatings which are defective andunsatisfactory, by reason of the presence of streaks, scratches and other coating defects. Accordingly, although the conventional Trist-type coater has been rather widely used, its use universally has been limited to the application of light coat weights, usually in the range of 3 to 5 pounds per ream.

In accordance with one aspect of the present invention, the coating blade, which may be strip of spring steel about 3 /2 inches wide and 146 inches long and which is provided with a blade face formed at predetermined angles to the principal blade surfaces, is provided with a novel configuration at the blade tip, such that improved coating performance is realized and blade life is increased by a factor of ten to twenty times. In a blade of known design, the blade thickness usually is relatively small, and the blade face is ground at an acute angle, approximating the wear angle, to the lower blade surface. In operation, the blade face is subject to the relatively abrasive action of the paper web and of the coating material itself. This tends to cause rapid wear of the blade face, such that, after a relatively short period of operation, the tip of the blade has a thin wire edge formed thereon. Ultimately, this causes the presence of streaks and scratches, as well as beading of the coating material at the blade tip, resulting in sub-standard quality in the coated paper. Accordingly, as one of the specific aspects of the invention, the angled face of the blade is modified at its tip in a novel manner, to obviate these problems and, at the same time, to increase significantly the operating life of the blade. This advantageous result is realized by grinding off this sharp tip of the blade such that the new apex of the blade tip extremity lies between the principal planes of the blade, rather than in the plane of the lower blade surface. Further, the modification of the blade tip is so carried out that the angle now formed by the tip of the blade, hereinafter referred to as the toe angle, is caused to lie substantially within a range of angles of 60 to 90 degrees.

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Two important benefitsare realized by utilizing a blade tip: configuration as described in the foregoing paragraph. First, the operating life of the blade is increased ten to twenty fold, as compared to conventionally ground blades. Second, the qualityof coating work is materially enhanced by use of the blade, in respect of both mechanical. and operating? defects. Mechanical defects frequently are caused by nicks and gouges in the blade, and these are reduced significantly by the new blade tip configuration. Operating defects result from, among other things, the wearing of the. tip to form a wire edge in the formation of a bead of coatingrnatd rial behind the blade tip, and defects of this sort also are materially reduced by the new configuration.

A further specific aspect of the. invention resides in an improved heel configuration oftheblade-edge, affording a significant reduction in operatingdefects caused by foreign particles lodging about the blades edge'or forming pits at and about the heel of the blade, the heel being defined as the upper edge orcorner areaof the working edge of the blade, In general, the improved heel configuration is provided byforming orapproximating an arcuate surface at the heel edge having a radius in the range of 0006-0008 inch.

A further and significant aspect of the invention'resides in the provision of a coating blade of the type referred to and advantageously having. the improved tip and heel configurations described above which is provided on its operative surfaces with a chrome plating. of optimum thickness. The improved blade thus provided has several significant advantages, First, its operating life is increased five to ten times, as compared to a similar blade not so plated on its operative surfaces. Second, the blade is smoother, accommodatingthe freer passage of foreign particles past the blade edge and thereby materially reducing streaks and scratches. Third, the operative surfaces of the plated blade are hard and impervious, whereas similar, unplated surfaces of similar blades have a definite. microscopic porosity, which promotes the lodging of foreign particles and results in undesirable scratching and streaking of the. coating.

For a better understanding of the invention and for a discussion of the above and other features and advantages thereof, reference should be made to the following detailed description' and to the accompanying drawing, in which:

FIG. 1 is a simplified cross sectional view of an advantageous form of trailing blade coater inco-nporating the improved blade of the invention; and

FIG. 2 is an exaggerated view of the working edge of the improved blade showing the approximate configuration of the roll with the blade in position.

Referring now to the drawing, the reference numeral 10 designates generally a blade coater. The blade coater comprises a backing roll 11, provided with a resilient surface covering 12, about which a web 13 is passed for coating. A reservoir 14 is mounted in operative relation to the backing roll 11, such that the web 13 passing about the roll forms, in effect, one wall of the reservoir.

Advantageously, th reservoir 14 comprises a back wall 15, a bottom wall 16, and a smoothly curved transit-ion wall 17 connecting the back and bottom walls. A pair of end dykes 18, pnovided with felt peripheral seals 19, are positioned at each end of the reservoir. The dykes are in operative contact with the web 13, and with the walls of the reservoir, whereby the reservoir forms an effective enclosure for supply 20 of coating material. The configuration of the reservoir is such as to permit pro-per circulation of the coating material during operation of the coater.

Outlet ducts 21 may be located at definite areas of the reservoir, for withdrawing coating material laden with concentrations of foreign particles. The withdrawn material is filtered, and the filtered material, together with additional material for make-up, is returned to the reservoirs through a duct 22, for example, so that the reservoir supply remains relatively constant.

The bottom wall of the reservoir is formed in part by coating blade 23, mounted iadjustably between the bottom wall 16 and a clamping plate 24, which guide the blade and also an adjusting slide 25 therefor. As shown in FIG. 1, the blade is supported at a principal angle of 40 to 5 0, measured between the plane of the supported portion of the blade and the plane tangent to the surface of the backing roll along the line of intersection of that surface with the support plane of the blade. In mounting the blade at this angle, two procedures may be followed. In one procedure the blade may be temporarily brought into kissing contact with the roll surface when setting up the machine for operation and before the web is passed around the backing roll. Since there will be no distortion of the backing roll, the plane tangent to the backing roll surface can be calculated and the mounting angle. measured. After the blade is set at the desired angle, it may be moved further into contact with the roll surface as shown in FIG. 1. Alternatively, the blade may originally be brought into contact with the roll surface with the end of the blade deflected as shown in FIG. 1. Since the distortion of the roll surface is minute, it may be disregarded in calculating an approximate plane tangent to the roll surface at this point of contact. As previously stated, the principal angle may be between 40 and 50 and therefore, it can be seen that it is not critical if the plane used for measuring this angle is not exactly tangent to the roll surface. In addition, the blade is advantageously formed of spring steel, having a thickness of about 0.010 inch to 0.030 inch and an unsupported extension of about inch to 1% inches. In the operation of the coater, the blade bears with a predetermined amount of force against the web 13 and backing roll, causing the unsupported extension of the blade to be deflected downward, as illustrated in FIG. 1.

In accordance with the present invention, improvements are made on the blade 23 itself. Blade 23 is provided with an improved tip configuration, the principal effect of which is to increase the operating life of the blade by a factor of or times, over blades of conventional configuration, and a secondary effect of which is to provide a general improvement in the coating quality. Referring particularly to FIG. 2 of the drawing, there is shown the extended or operating edge of the blade 23, the blade having upper and lower principle surfaces 26-27 and a working surface 28 disposed at an acute angle with respect to the lower blade surface 27. This angle, termed the wear angle, is measured at the intersection of the extension of the surfaces 27 and 28 and has a value of less than 40". As shown in FIG. 2, it is designated by A. The orientation of the blade 23 is such that the working surface 28 faces the backing roll 11. In accordance with prior practice, at least in connection with a trailing blade apparatus as shown in FIG. 1, the working edge of the blade 23 was ground, prior to installation of the blade, so that the working surface 28 extended from the lower surface 27 of the blade to its upper surface 26. Typically, the surface 28 may be preground to an initial blade surface angle 29 to 31 with respect to the lower principal surface 27. Usually, at least with blades not incorporating certain other features of this invention yet to be described, a newly installed blade is run in for a few minutes, using an abrasive material, to smooth the blade and conform it more accurately to the surface of the backing roll and web under actual operating conditions. The run in period and the subsequent normal operation of the equipment may cause the blade to assume a normal wear angle of less than 40 and preferably about 33.

In a blade of known configuration, the working tip 29 of the blade, encompassing an angle of about 33, tends to form a wire edge, and the presence of such a wire edge soon causes the coating quality to be sub-standard, necessitating replacement of the blade. Presently, blades of known configuration and construction have an operating life equivalent to the coating of about ten tons of paper. In accordance with the invention, significant improvement in blade life and operation are realized by pregrinding the blade tip not only to form the usual working surface 28, but also by grinding off the blade tip extremity, so that the actual working tip of the blade lies between the principal surfaces of the blade, rather than substantially in the plane of the lower surface. In the new and improved blade configuration, shown in FIG. 2, the actual working tip 29 of the blade is ground back considerably, advantageously to a point spaced about 0.008 inch from the surface 27 and about 0.017 inch from the surface 26, in a blade having a total thickness of 0.025 inch.

In grinding back the working tip extremity of the blade there is formed a bottom surface 30, which extends from the working surface-28 of the blade to the lower surface 27 thereof. The angle formed at the intersection of the bottom surface 30 and the blade working surface 28 is shown in FIG. 2 as B and may be termed the toe angle. This toe angle is significant, and should not be substantially less than 60. In this connection, it has been found that a smaller toe angle B will render the blade subject to the formation of a wire edge so that blade life improvement is minimized. Similarly, it has been found that the toe angle B is subject to a practical maximum limitation, depending somewhat upon the rheological properties of the coating material. Our present experience with certain frequently used coating materials, indicates that the toe angle B should not be substantially greater than The consequences of providing a greater toe angle, with the usual coating materials, are that beading (formation of small droplets of coating material on the bottom surface 30 of the blade) will occur. Such beading is very undesirable and detrimentally effects coating qualities.

Usually, although not necessarily, the working surface 28 is ground prior to the grinding of the bottom surface 30. The actual technique of grinding appears to be significant, and experience indicates that thedirection of the grind should be from the tip extremity toward the back of the blade or, alternatively, parallel to the length of the blade. Grinding in the direction from the back of the blade toward the tip extremity usually results in the formation of wire edge at the working tip and is undesirable for that reason.

A blade modified by grinding back the working tip extremity in accordance with the invention has an operating life 10 to 12 times greater that that of a blade similar in all other respects. Such significant improvement is believed to result in large part from the fact that substantial blade wear can occur at the blade tip extremity without the formation of a Wire edge. This is particularly important where the pre-ground angle of the blade surface 28 is smaller than the actual wear angle such that, initially at least, substantially more wear takes place at the blade tip extremity than over the rest of the working surface 28. A further advantage of the improved configuration resides in the fact that the blade tip extremity 2? by reason of its significant toe angle, is less subject to acquiring nicks and gouges in the initial handling, assembly, etc., such that coating quality is improved generally, and less run in of the blade is required.

In accordance with another specific aspect of the invention, improvements are effected in the configuration of the heel of the blade, that is, the upper corner area of the Working surface 28. In accordance with the invention, the blade heel is rounded very slightly, and such slight rounding enable significant improvements to be realized. In a typical coating blade having a thickness .5 of about 0.025 inch, the heel R is rounded on an arc having a radius in the range of 0.006 to 0.008 inch And, in this respect, although the true arc is believed to be more ideal, it appears to be sufficient, from a practical standpoint, to approximate the specified are by grinding one or more flat bevels at the heel edge formed by the blade surfaces 26 and 28.

Experience indicates that a 'blade having the modified and improvedheel configuration described above affords significant improvements in coating quality.

Thus, in the operation of a blade coater of the type shown in FIG. 1, the web 13 moves downward at very high speed (e.g., 2500 feet a minute) and causes the body of coating material in'the reservoir to circulate at high'velo'cities. Substantial momentum is developed by the particles in -the'coating material, by reason of such high circulation velocities, and this causes the particles to actually impinge on the metal of theblade. This results inthe formation of pits in the heel area of the blade which, in turn, causes streaks in the coated web, with a possible reduction inthe quality of the output.

An additional significant advantage derived from the improved heel configuration is a noticeably decreased tendency for beading to occur when the blade is run close to its heel. The reason for such decreased beading tendencies, realized from the improved heel configuration, is not clearly understood at this time.

A further specific feature of the invention resides in the provision of an improved blade for a blade coater, in which a chrome plated surface is provided about the effective area of the blade edge. More specifically, the effective or active areas of the blade, immediately adjacent and including the working surface are provided with a hard, smooth chrome plating or predetermined thickness.

A blade having chrome plated working surface areas in accordance with the invention affords significant advantages in respect of operating life of the blade, coating quality and machine run in time. By way of example, a blade having the modified configuration heretofore described will produce up to 35 rolls of paper, equivalent to over 100 tons. The same blade, provided with the improved chrome plated operating surface areas will produce up to 500 to 1000 tons of paper, corresponding to an increased operating life of to times, compared to a similar blade with ordinary surfaces.

A secondary, but nevertheless important advantage of the chrome plated blade resides in the improved quality of the coated paper. The chrome plated surfaces, including particularly the working surface 28 and the adjacent areas of the upper blade surface 26, are considerably smoother and harder when chrome plated than otherwise, such that the blades pass foreign particles with significantly increased efiiciency, resulting in fewer scratches and streaks in the coated sheet. In part, the improvement in coating quality, realized through the use of blades having chrome plated effective surface areas, is believed to result from the fact that the chrome plating closes microscopic pores in the spring steel blades, so that particles do not imbed themselves in the blade or otherwise tend to adhere thereto in the vicinity of the blade tip. The smoother surfaces of the blade, moreover, not only provide for the more efficient passage of particles but also provide a smoother flow of the coating material generally whereby the general improvement in the quality of coating is realized.

The use of a coating blade provided with chrome plated effective surface areas is also advantageous from the standpoint that the polishing of the blade surfaces may be substantially completed off of the coating machine, so that run in time is significantly reduced and quality improvement in the initial portions of the coating runs is realized.

Although the critical limits of chrome plate thickness are not known with exactitude, present experience indicates that the plating should be in the range of 0.0003 to 0.0030 inch. Extreme thinness of the coating is, of course, undesirable as since the substantial benefits of the coating will not be fully realized. At the same time, excessively thick coatings are undesirable, in that the plating tends to build up on sharp edges and round them off in an undesirable manner.

The various improvements effected by this invention cooperatively result in truly outstanding improve ment in the operating life of the blade, as well as in the quality of the coated sheet. The combined improvement and operating life resulting from the described improvements is in the order of one hundred fold, the significance of which may be appreciated when considering that coating speeds usually are in excess of 2,000 feet per minute and down time for blade changes usually is over an hour.

It should be understood that the specific form of the invention herein illustrated and described is intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention:

I claim:

1. In a trailing blade coater of the type comprising a backing roll about which a web is passed, a reservoir body for coating material positioned cooperatively with respect to said backing roll, and a trailing blade having a principal plane and a working surface forming, in effect, a portion of the bottom wall of said reservoir body, said backing roll, reservoir, body and blade cooperatively forming a reservoir for holding a supply of coating material, said blade having a normal wear angle less than 40 being mounted at an angle of about 4050 with respect to a plane which is tangent to the surface of the backing roll and extends through the point of intersection of the principal plane of the blade with the backing roll surface, the improvement characterized by said blade being formed to have a toe angle of not substantially more than nor substantially less than 60.

2. The apparatus of claim 1, in which said blade has a heel radius of between about 0.006 and 0.008 inch.

3. The apparatus of claim 1, in which the Working surface of said blade has a chrome plate surface layer of 0.0003 to 0.0030 inch thickness.

4. In a blade coater having a blade mounted to bear against a travelling web, said blade having a normal wear angle of less than 40 and a working surface, the improvement characterized by said blade having a toe angle of not substantially more than 90 nor substantially less than 60.

5. The apparatus of claim 4, in which said blade has a heel radius of between about 0.006 and 0.008 inch.

6. The apparatus of claim 4, in which the working surface of said blade has a chrome plate surface layer of 0.0003 to 0.0030 inch thickness.

7. In a trailing blade coater of the type comprising a backing roll about which a web is passed, a reservoir body for coating material positioned cooperatively with respect to said backing roll, and a trailing blade having a principal plane, a lower principal surface and a bottom surface, said blade forming, in effect, a portion of the bottom wall of said reservoir body, said backing roll, reservoir body and blade cooperatively forming a reservoir for holding a supply of coating material, said blade having a working surface facing said backing roll and being mounted at an angle of about 4050 with respect to a plane which is tangent to the surface of the backing roll and extends through the point of intersection of the principal plane of the blade with the backing roll surface, the improvement characterized by said blade having a normal wear angle defined by the extension of the lower principal surface and the working surface of less than 40, and a toe angle defined by the working surface and 7 the bottom surface of substantially no more than 90 nor substantially less than 60.

8. The apparatus of claim 7, in Which said blade has a heel radius of between about 0.006 and 0.008 inch.

9. The apparatus of claim 8, in which said blade has ,7

a chrome plate of about 0.0003 to 0.0030 inch thickness upon the Working surface and the bottom surface.

10. In a blade coater having a blade provided with a working surface, a lower principal surface and a bottom surface mounted to bear against a travelling web such that the working surface of said blade faces said web, said blade having a normal wear angle defined by the extension of the lower principal surface and the working surface of less than 40, the improvement characterized by said blade having a toe angle defined by the Working surface and the bottom surface of substantially no more than 90 nor substantially less than 60.

11. The apparatus of claim 10 in which said blade has a thickness in the order of 0.025 inch and a heel radius of between about 0.006 and 0.008 inch.

12. The apparatus. of claim 11 in which said blade has a chrome plate of about 0.0003 to 0.0030 inch thickness upon the working surface and the bottom surface.

References Cited by the Examiner UNITED STATES PATENTS 396,711 1/1889 Richards. 1,993,055 3/1935 Gerstenberg. 2,051,403 8/1936 Boyer et al. 10 2,185,223 1/1940 Paynter.

2,213,117 8/ 1940 Blackmore. 2,27 1,458 1/ 1942 Lionne. 2,695,004 12/1954 Montgomery et al. 2,754,796 7/1956 Faulkner et1al. 15 2,918,899 12/1959 Munton et al. 118-259 x FOREIGN PATENTS 470,144 12/ 1950 Canada. 4

20 CHARLES A. WILLMUTH, Primary Examiner.

RICHARD D. NEVIUS, Examiner. 

1. IN A TRAILING BLADE COATER OF THE TYPE COMPRISING A BACKING ROLL WHICH A WEB IS PASSED, A RESERVOIR BODY FOR COATING MATERIAL POSITIONED COOPERATIVELY WITH RESPECT TO SAID BACKING ROLL, AND A TRAILING BLADE HAVING A PRINCIPAL PLANE AND A WORKING SURFACE FORMING, IN EFFECT, A PORTION OF THE BOTTOM WALL OF SAID RESERVOIR BODY, SAID BACKING ROLL, RESERVOIR, BODY AND BLADE COOPERATIVELY FORMING A RESERVOIR FOR HOLDING A SUPPLY OF COATING MATERIAL, SAID BLADE HAVING A NORMAL WEAR ANGLE LESS THAN 40* BEING MOUNTED AT AN ANGLE OF ABOUT 40*-50* WITH RESPECT TO A PLANE WHICH IS TANGENT TO THE SURFACE OF THE BACKING ROLL AND EXTENDS THROUGH THE POINT OF INTERSECTION OF THE PRINCIPAL PLANE OF THE BLADE WITH THE BACKING ROLL SURFACE, THE IMPROVEMENT CHARACTERIZED BY SAID BLADE BEING FORMED TO HAVE A TOE ANGLE OF NOT SUBSTANTIALLY MORE THAN 90* NOR SUBSTANTIALLY LESS THAN 60*. 